*{
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

a{
  display: block;
  text-decoration: none;
  // 继承父元素的字体颜色  div一样 
  color: inherit;
}
img{
  // 3px
  display: block;
  // 让图片的大小由父元素来控制
  width: 100%;
}

ul{
  list-style: none;
}

.clearfix::after{
  content: "";
  display: block;
  height: 0;
  line-height: 0;
  visibility: hidden;
  clear: both;
}
input,button{
  border: none;
  outline: none;
}